Notch-Mediated Epigenetic Regulation of Voltage-Gated Potassium Currents.

Abstract

Ventricular arrhythmias often arise from the Purkinje-myocyte junction and are a leading cause of sudden cardiac death. Notch activation reprograms cardiac myocytes to an induced Purkinje-like state characterized by prolonged action potential duration and expression of Purkinje-enriched genes. To understand the mechanism by which canonical Notch signaling causes action potential prolongation. We find that endogenous Purkinje cells have reduced peak K⁺ current, I_to, and I_K,slow when compared with ventricular myocytes. Consistent with partial reprogramming toward a Purkinje-like phenotype, Notch activation decreases peak outward K⁺ current density, as well as the outward K⁺ current components I_to,f and I_K,_slow. Gene expression studies in Notch-activated ventricles demonstrate upregulation of Purkinje-enriched genes Contactin-2 and Scn5a and downregulation of K⁺ channel subunit genes that contribute to I_to,f and I_K,slow. In contrast, inactivation of Notch signaling results in increased cell size commensurate with increased K⁺ current amplitudes and mimics physiological hypertrophy. Notch-induced changes in K⁺ current density are regulated at least in part via transcriptional changes. Chromatin immunoprecipitation demonstrates dynamic RBP-J (recombination signal binding protein for immunoglobulin kappa J region) binding and loss of active histone marks on K⁺ channel subunit promoters with Notch activation, and similar transcriptional and epigenetic changes occur in a heart failure model. Interestingly, there is a differential response in Notch target gene expression and cellular electrophysiology in left versus right ventricular cardiac myocytes. In summary, these findings demonstrate a novel mechanism for regulation of voltage-gated potassium currents in the setting of cardiac pathology and may provide a novel target for arrhythmia drug design.